Kato H, Sumimoto H, Pognonec P, Chen C H, Rosen C A, Roeder R G
Laboratory of Biochemistry and Molecular Biology, Rockefeller University, New York, New York 10021.
Genes Dev. 1992 Apr;6(4):655-66. doi: 10.1101/gad.6.4.655.
The HIV-1 trans-activator Tat increases the rate of transcription from the HIV-1 LTR promoter through the stem-loop-containing TAR RNA. To analyze the mechanisms of Tat action, a cell-free trans-activation system with no preincubation has been developed. Recombinant Tat specifically increased the level of a long runoff transcript but not a promoter-proximal transcript in a TAR-dependent fashion. These observations and the result of pulse-chase experiments support strongly the hypothesis that Tat enhances the ability of RNA polymerase to elongate over longer distances. Increased levels of the purified cellular factor TFIIF, essential for initiation and also implicated in elongation of transcription, obviated trans-activation by Tat by increasing the basal (Tat-independent) activity. However, another elongation factor, ATN/TFIIS, showed synergistic activation with Tat. An antiserum against a recombinant form of the large subunit of TFIIF (RAP 74) preferentially suppressed the activated level of transcription exerted by Tat. We propose the hypothesis that Tat acts as a processivity factor on RNA polymerase II in an analogous manner to TFIIF.
HIV-1反式激活因子Tat通过含茎环结构的TAR RNA提高HIV-1长末端重复序列（LTR）启动子的转录速率。为了分析Tat的作用机制，已开发出一种无需预孵育的无细胞反式激活系统。重组Tat以TAR依赖的方式特异性提高了长延伸转录本的水平，但未提高启动子近端转录本的水平。这些观察结果以及脉冲追踪实验的结果有力地支持了以下假设：Tat增强了RNA聚合酶进行长距离延伸的能力。纯化的细胞因子TFIIF水平升高，它对转录起始至关重要且也与转录延伸有关，通过增加基础（不依赖Tat）活性消除了Tat的反式激活作用。然而，另一种延伸因子ATN/TFIIS与Tat表现出协同激活作用。针对重组形式的TFIIF大亚基（RAP 74）的抗血清优先抑制了Tat施加的激活转录水平。我们提出以下假设：Tat以与TFIIF类似的方式作为RNA聚合酶II的持续合成因子。
